1) Are you sure you want to be on Server Fault and not on Super User? 2) If I understand you correctly then installing works fine, but when you boot the new OS after it is installed then the bootloader can not the disk to mount / from ?
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HennesNov 30 '13 at 0:13

And to do the installation, the error appears. Not yet installed freebsd.
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user628298Nov 30 '13 at 0:29

This is really something you should take up with the FreeBSD folks (politely please). If this is your first time using FreeBSD the EFNet #FreeBSDHelp IRC channel would be a good place to ask. At first glance however Kindule appears to be correct: You've somehow managed to screw up creating your installation media. Review the instructions in the handbook for more information.
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voretaq7♦Nov 30 '13 at 8:27